This invention relates to an improved process for reacting allyl chloride, water and chlorine to produce dichlorohydrin. "Dichlorohydrin" is a term employed herein to designate the isomers 1,2-dichloro-3-hydroxypropane and 1,3-dichloro-2-hydroxypropane.
It is known to prepare an aqueous solution of dichlorohydrin by reacting in a reaction zone allyl chloride, water and chlorine in a dilute aqueous phase. U.S. Pat. No. 2,714,121, incorporated herein by reference, discloses producing halohydrins by using high dilution of, e.g., 250-400 volumes of water per volume of, e.g., a halosubstituted hydrocarbon in aqueous medium with subsequent addition of the halogen, and keeping the organic by-product phase dispersed as fine particles. U.S. Pat. No 2,714,123, incorporated herein by reference, discloses producing an aqueous solution of dichlorohydrin in a series of reaction stages wherein substantially all of the water is fed to the first reaction stage and the other reactants are added in substantially equimolar proportions into each of the subsequent reaction stages.
The reaction zone effluent may be worked up in various ways to recover the dichlorohydrin therefrom, or may be processed further in an integrated process to convert the dichlorohydrin to derivatives such as epichlorohydrin and/or glycerine.
It is known, e. g., from Belgian Pat. Nos. 614,890 and 614,891 that dichlorohydrin may be extracted from aqueous solution with organic solvents such as phosphate esters of aliphatic monohydric alcohols containing more than four carbon atoms, aryl phosphates, and liquid aliphatic alcohols and liquid ketones having 8 to 18 carbon atoms per molecule. U.S. Pat Nos. 4,620,911 and 4,665,240 disclose as further solvents for dichlorohydrin saturated aliphatic ethers and chlorinated hydrocarbons containing up to about 9 carbon atoms, including, e.g., carbon tetrachloride. The aforesaid U.S. Pat. Nos. 4,620,911 and 4,665,240 employ solvent extraction together with membrane processes to reduce the amount of fresh water fed to the reaction zone of the process.
One disadvantage of the known processes is the formation of undesired by-products, which reduce the overall efficiency of the process and may complicate purification procedures of the desired product. Such conventional processes result in an aqueous effluent stream which contains minor amounts of organic impurities diluted in a substantial amount of water. Such effluent requires energy intensive treatment to reduce the amount of organic materials to levels acceptable to be passed to receiving bodies of water such as rivers, lakes and the like. Considerable savings could be effected if the amount of organics to be treated could be significantly reduced.
A further disadvantage of the known processes is that polychlorinated alkane byproducts are formed during the aqueous dichlorohydrin synthesis. When, as is often the case, it is desired to further convert the dichlorohydrin to epichlorohydrin (1,2-epoxy-3-chloro-propane) in a subsequent step by the action of basic reagents, said byproducts are dehydrochlorinated to form chloroaliphatic impurities which have volatility close to epichlorohydrin. These impurities, although removable by conventional fractional distillation procedures, require inordinate input of energy to achieve epichlorohydrin purity required for a number of demanding end-use applications. The present invention advantageously substantially removes the precursor impurities from the dichlorohydrin prior to conversion to epichlorohydrin and in a manner which is much more energy efficient than finishing of epichlorohydrin by conventional distillation.
A method has now been found to reduce the level of chloraliphatic alkanes and chloraliphatic ethers impurities in the dichlorohydrin product and to obtain said impurities in relatively concentrated form for further processing or disposal.